Method and compositions for stabilizing incompetent oil-containing formations

ABSTRACT

Improved method of and compositions for the treatment of an oilcontaining incompetent formation to prevent the movement of unconsolidated sand particles in an underground formation by forming a treating composition of sand, cement, silica flour, and a sufficient amount of petroleum oil fraction containing an oilwetting agent therein to oil-wet the sand, cement, and silica flour particles, suspending the resulting treating composition in an aqueous carrier medium, injecting the aqueous suspension against the unconsolidated formation at a pressure effective to force the treating composition into contact with the unconsolidated formation, contacting the placed treating composition with an aqueous surface active agent solution to water wet the cement particles, permitting the cement to set and form a permeable cement and recovering oil through the cement.

lob-90o AU 112 EX United States ratent Curtice et al.

[ 51 Mar. 7, 1972 [54] METHOD AND COMPOSITIONS FOR STABILIZINGINCOMPETENT OIL- CONTAINING FORMATIONS 721 Inventors: Beverly A.Curtlce; Bobby 6. limsberger, both of Houston, Tex.

[73] Assignee: Texaco Inc, New York, NY.

[22] Filed: June 8, 1970 [21] Appl. N0.: 44,550

3,368,623 2/1968 Carteretal ..l66/276 3,467,193 9/1969 Messenger..l66/294X Primary Examiner-Stephen J. Novosad Auomey-Thomas l-l.Whaley, Carl G. Reis and James F. Young [57] ABSTRACT Improved method ofand compositions for the treatment of an oil-containing incompetentformation to prevent the movement of unconsolidated sand particles in anunderground formation by forming a treating comwition of 5 m, cement,j]- ica flour, and a sufiicient amount of petroleum oimtion,eliflll'iing an o ilwettin a ent then-chm men an silm suspending theresulting treating composition in an uous l urn, injecting the aqueoussuspension against efiinonso l a'ted formation at a pressure efi'ectiveto force the treating composition into contact with the unconsolidatedfonnation, contacting the placed treating composition with an aqueoussurface active agent solution to water wet the cement particles,permitting the cement to set and form a permeable cement and recoveringoil through the cement.

12 Claims, No Drawings METHOD AND COMPOSITIONS FOR STABlLlZINGINCOMPETENT OIL-CONTAINING FORMATIONS The present invention relates tothe treatment of permeable underground formations. More particularly,the present invention relates to an improved method of treatingpermeable underground unconsolidated sand-containing formations andparticularly oiland/or gas-containing unconsolidated sand formations tostabilize the sandy portion thereof and to an improved treatingcomposition useful in the stabilization of such incompetent sandcontaining underground formations.

The recovery of fluids such as, for example gas and/or oil fromunderground formations has been troublesome in areas wherein theunderground formation is composed of one or more incompetentsand-containing layers or zones. The sand particles in the incompetentzone and/or layer tend to move or migrate to the well bore duringrecovery of the formation fluids from the particular zone and/or layerand frequently the moving sand particles block the passageways leadingto the well bore. Plugging or materially impairing the flow of theformation fluids toward the bore hole results in a loss of these fluidsto the producer or so decreases the rate of fluid recovery from the wellas to cause the well to be shut down because it is economicallyunattractive to continue to produce therefrom. An additional adversefactor resulting from the movement of the sand particles toward the wellbore is that they are often carried along with the formation fluids tothe well bore and passed through the pipes, pumps, etc., being used torecover the formation fluids to the surface with resulting damage to themoving parts thereof as the sand particles are very abrasive.

Many attempts have been made heretofore to prevent or decrease the flowof undesirable sand particles in the formation and/or in the productiontubing and associated equipment, such as by the placement of sandscreens, filters, liners, and so forth, These prior attempts have beenunsuccessful for a number of reasons among which is that thesemechanical devices fail to prevent completely the flow of the formationparticles into the production equipment. In addition these devicesinterfere with various types of completion and workover operations. Inrecent years, the industry has attempted to avoid the difficultiesencountered in the use of mechanical devices by employing variouschemical compositions to effect consolidation of the undergroundincompetent formations. These methods have generally consisted ofinjecting into the underground formation polymerizable resinousmaterials which when subsequently polymerized form permeable barriers inthe formation to prevent the sand particles from movement therethrough.However, this technique of sand consolidation has not met withwidespread acceptance because of the inherent difficulties of effectingpolymerization of the resinous materials in the formation to a degreesufficient to consolidate these underground formations and yetpermitting the unobstructed flow of the desirable formation fluidstherethrough. Further, the cost associated with these resin coatingmethods has been relatively high in comparison with the prior mechanicalmethods.

It is known from commonly assigned US. Pat. No. 3,429,373, issued Feb.25, 1969, titled Method and Composition for Stabilizing Incompetent OilContaining Formations" to form a slurry of sand, cement and a sufficientamount of a petroleum oil fraction containing an oil wetting agenttherein to oil wet the sand and cement particles, suspending the oil wetsand and cement particles in an aqueous carrier medium, injecting theaqueous suspension against the unconsolidated sand formation, contactingthe suspension with an aqueous surface active agent solution to waterwet the cement particles, permitting the cement to set and form apermeable cement and recovering oil through the cement.

By the improved method and composition of the present invention one isable to treat more effectively the underground formation to bestabilized in a rapid and efficient manner.

One object of the present invention is to provide an improved method oftreating underground sand-containing formations to stabilize theincompetent formation. An additional object is to provide afluid-permeable barrier between the formation sand and the well bore toprevent or to minimize the flow of unconsolidated sand particlestherethrough while maximizing the flow of desired fluids andparticularly petroleum hydrocarbons therethrough. A still further objectis to provide an improved novel treating composition for use instabilizing incompetent sand formations and to a method of placing sameto form a permeable cement filter against the incompetent formation.

How these and other objects of the invention are accomplished willbecome apparent with reference to the accompanying disclosure. in atleast one embodiment of the method of this invention at least one of theforegoing objects will be obtained.

It has now been discovered that an improved method of treating anincompetent sand containing underground formation comprises introducingagainst said formation a particular treating composition consistingessentially of a hydrocarbon oil wet sand, cement, oil-wetting agent andfinely ground silica dispersed or suspended in an aqueous carrier mediumin an amount sufficient to stabilize the formation and then to contactthe introduced treating composition with an aqueous solution of ahydrophilic surfactant to penetrate the oil layer about the sand, cementand finely ground silica components of the treating composition and toeffect setting of the cement to form a fluid-permeable barrier betweenthe formation and the well bore. The resultant formed permeable cementbarrier serves to prevent or to materially reduce the flow of theunconsolidated sandy particles therethrough while permitting the flow ofdesirable formation fluids through the permeable barrier at asubstantially unimpaired rate.

in carrying out the improved method of the present invention thetreating composition suspended in the aqueous carrier medium can bepumped down the well bore preferably under sufficient pressure to forcethe hydrocarbon oil-wetted sandcement-oil-wetting agent finely groundsilica admixture against the unconsolidated formation adjacent to or inreasonable proximity to the well bore. When the treating composition isplaced against the formation to be consolidated the treating compositionthen is contacted with an aqueous solution of a hydrophilic surfactantwhich displaces the oil layer around the sand-cement-finely groundsilica particles and renders these particles water wet. The cementcomponent of the composition then sets up and hardens. After the cementhardens the well can be equipped for production and the formation fluidscan be recovered by passing through the result-- ing formed permeablecement barrier into the well bore and recovered therefrom without theformation fluids being contaminated with the presence therein ofunconsolidated sand particles.

The improved method of the present invention is particularly adaptablefor use in any type of well completion but is generally used in a wellwherein casing has been set and which has perforations therein at thedesired intervals behind which the unconsolidated formation sands arelocated. Packers can be initially set above and below the perforatedintervals to prevent the treating composition from passing into thenonisolated portions of the well and also to permit buildup ofsufficient pressures on the treating composition to force same throughthe perforations and against the formation without plugging up the wellbore. After the treating composition has been forced through the casingperforations and against the formation and after it has been contactedwith the aqueous solution of the hydrophilic surfactant the well isclosed in to permit the cement to set and form the permeable cementbarrier for the unconsolidated sand in the formation.

The treating composition useful in the method of the present inventionmust meet certain specific requirements. The sand component in generalshould be closely sized in the broad range 12-80 mesh, i.e., l2-20,20-40, 40-60, or intermediate meshes, to permit effective relativelyhigh-permeability cement barriers being formed. In addition, the ratioof the sand component to the cement component should be about threeparts to about l2 parts by weight of sand per part of cement. It hasbeen found that a frac sand, i.e., a sand customarily used information-fracturing operations, having a size of between about and 40mesh is most suitable for use in the cement slurry of the presentinvention. It is preferred to use a graded sand with the larger grainsbeing not more than about twice the diameter of the smaller grains,i.e., 12-20 mesh, 20-40 mesh, 40-60 mesh, etc. In general, a 20-40 meshsand is used because of its ready availability and adaptability for usein stabilizing most formations In addition, the use of a 20-40 mesh sandappears to prevent premature bridging which is likely to be moreprevalent with finer mesh sands. Sand particles which are coarser thanabout 12 mesh and finer than about 80 mesh are unsuitable for use in thecomposition of the present invention. The coarser particles are notsatisfactory because the resultant set cement barrier has too great apenneability to prevent the flow of very fine unconsolidated sandparticles therethrough when the well is placed on production. Very finesand particles, that is those sand particles finer than about 80 mesh,are unsuitable because the resultant set cement has too low apermeability to permit the flow of desired formation fluidstherethrough.

The cement component of the composition of the present invention shouldbe present in the composition in a ratio of about one part of cement tofrom three to about twelve parts by weight of sand, on a weight basis.The cement component of the composition of the present invention may beany of the cements normally used in oil well cementing operations aswell as plaster of par-is cement. lt is preferred that the cementcomponent be a lightweight Portland cement having a density of about 75pounds per cubic foot and a chemical analysis approximately as follows:silicon dioxide 38.3%, aluminum oxide 13.0%, ferric oxide 5.2%, calciumoxide 35.7%, magnesium oxide l.6%, and sulfur trioxide 2.4%, with a losson ignition of approximately 3.3%. This particular lightweight Portlandcement has been found to be most suitable in the composition of thepresent invention since permeable cements made from this cement are moststable to attack by formation brines containing sodium chloride orsodium sulfate. Other oil well cements are not as resistant to attack byformation brines or sulfate solutions and therefore are not as practicalfor use in the cement composition of the present invention. These othercements appear to lose some of their compressive strength and becomeeroded from contact with sodium chloride and sodium sulfate solutions.In contrast the cements of the composition of the present invention arevery resistant to erosion by sodium chloride or sodium sulfate solutionsand do not lose their compressive strengths even after prolongedexposure thereto.

The finely ground silica component of the composition must be of a sizesufficient to pass through the openings of a No. 200-325 sieve (U.S.Sieve Series), i.e., a sieve having openings of 0.0029-0.00l7 inch. Thefinely ground silica component is employed in an amount of from about001 part to about 0.30 part, preferably 0.02 to 0.04 part, by weight perpart by weight ofcement.

T' ldlfiwcomponent of the composition should be employed in an amount offrom about 0.3 part to about 0.7 part by weight per part by weight ofcement. It is preferred that the oil component be employed in an amountof about 0.35 to about 0.45 part by weight per part by weight of cement.Use of the oil component in his amount provides sufficient oil to wetthe cement and sand components of the composition and at the same timeavoids an excess thereof which might damage the unconsolidatedunderground formation by the cement component being dispersed from thesand component when the composition is placed adjacent thereto.

Suitable hydrocarbon oils include the kerosene and diesel oil fractionsofa petroleum crude oil as well as refined oil fractions, and refinedmotor oils.

A necessary component of the petroleum oil fraction of the repellentagent, i.e., a water-insoluble oleophilic material of relatively highmolecular weight which will permit the petroleum fraction to oil wet thesurfaces of the sand, cement and finely ground silica particles in thetreating composition. The oil-wetting agent must contain an oleophilicgroup and a polar group for preferential adsorption on or at the oil andsand-cement interfaces. Representative oil-wetting agents useful in thepractice of the present invention include the relatively high molecularweight amines such as for example, the C -C hydrocarbylamines, decyl-,dodecyland octadecyl-amine, the C -C fatty alcohols such as cetyl andoctadecyl alcohol, the C -C alkylated phenols and naphthols, naturalfatty material such as lanolin, lard, cottonseed oil and fatty acidglycerides, amides such as the C,,C,, fatty acid amides, and mixtures ofthese oil wetting agents.

The oil-wetting agent is used in an amount of from about I to about 10percent by weight, based on the weight of the cement particles in thetreating compositions.

It has been found that a preferred procedure is to first dissolve theoil wetting agent in a solvent such as isopropyl alcohol, before mixingwith the oil component to facilitate mixing of these components.

The order of mixing the components of the treating composition isimportant. The sand, cement, oil, and oil-wetting agent components arefirst intimately mixed then the finely ground silica is added to thefirst admixture and further mixed. Failure to observe this procedurewill result in a decrease of the average compressive strength of thefonned permeable cement. It is preferred to mix the sand and cementcomponents separately, the oil and oil wetting agents separately, thenmix the two mixtures and finally to add the finely ground silica theretoand intimately admix the entire treating composition.

The aqueous carrier medium containing the suspended oil wet sand andcement solids is pumped down the well bore and into the formation to beconsolidated at a rate of from about I to 4 barrels of the suspendedsolids in the carrier medium per minute. Such pumping rates have beenfound to give the most satisfactory results in the practice of theinvention.

An aqueous surface active agent solution contacts the emplacedoil-wetted sand-cement particles to displace the oil therefrom and toinitiate hardening of the cement. The surface active agent used must bea water soluble material to penetrate the oil-sand-cement interface andwater wet the cement particles and remove the oil therefrom.Representative surface active agents that will perform satisfactorily inthe present invention include anionic, cationic and nonionic materialssuch as the alkyl, aryl, or alkaryl sulfates and sulfonates, thesulfated and sulfonated alkyloxyated amides, esters or ethers,hydrocarbylamine salts, esters or ether-esters of natural fats and oils,or alkyl phenols. The surface-active agents include polyoxyethylenesorbitan-monolaurate, monopalmitate, and -monooleate, oxyalkylated amylphenol, alkaryl polyether alcohols and polyoxyethylene ether. Apreferred surface active agent is an ethoxylated nonylphenol containingabout 9.5 moles of ethylene oxide, known by the trade name SurfonicN-95."

EXAMPLE l A mixture of 300 grams by weight of a frac sand known by thetrade name Ottawa" having a particle size of 2040 mesh and 67 grams of ahydraulic cement known by the trade name Trinity Lite Wate Cement wasprepared by intimately mixing the sand and cement. There was added tothe mixture with stirring 29 ml. of com otor oil containing 10 percentby volume of dodecylamine. The resulting stirred mixture of oil wetsolids was then mixed with 2 grams f finely ground silica flour of asize capable of passing throughm a NO. 325 sieve (openings 0.00l 7inch). The resultant admixture then was suspended in about 500 ml. ofsalt water (salt concentration l0 percent by weight). The suspension ofoil wet solids in the saline carrier was pumped at a pressure ofcomposition of the present invention is an oil wetting water 10-50p.s.i.g. intoatest cell measuring 3 inches in diameter by 6 inches inlength. The cell had been previously about half filled with packed sandparticles having a mesh size of 70300. The oil wet sand-cement-finelyground silica treating composition was filtered out of the salinecarrier liquid. Thereafter the sand pack was treated with 400 ml. of awater solution containing 1 percent of an ethoxylated nonylphenol havingan average of 9.5 ethylene oxide groups surface active agent known bythe trade name Surfonic N-95. The surface-active agent in the waterdisplaced the oil from the sand-cementfinely ground silica particles inthe pack and hydrated the cement. A hardened cement resulted after a24-hour waiting-on cement period. The water permeability of the hardenedcement was found to be about 8 darcies which was sufficient to block thefiow of very fine sand particles 'therethrough. The average compressivestrength of the cured cement was about 1,910 psi. A salt water solutioncontaining l0 percent by weight of salt was flowed through the permeablecement at a rate of 200 ml. per minute for a period of 14 weeks.Observations of the permeable cement after this period indicated nodecrease in its compressive strength.

COMPARATIVE EXAMPLE A The procedure of Example 1 above was repeatedexcept that no finely ground silica was added to the sand, cement, oil,and oil-wetting agent mixture.

The resulting cured permeable cement of this comparative example had acompressive strength of l,400 p.s.i. which decreased after beingsubjected to salt water flow-through for 2 weeks to about 480 psi.

Obviously, many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims. 1

We claim:

1. A method of treating an incompetent formation penetrated by a wellbore to prevent the movement of unconsolidated sand particles from saidincompetent formation to the well bore as formation fluids are recoveredfrom said formation which comprises forming a first treating compositionof cement, from three to 12 parts by weight of sand particles having amesh size of from about 20 mesh to about 80 mesh, from about 0.01 toabout 0.10 part by weight of an oil-wetting agent, and from 0.35 to 0.7part by weight of a petroleum oil fraction, each per part by weight ofcement, and adding to said first treating composition with mixing fromabout 0.02 to 0.04 part by weight per part by weight of cement of finelyground silica having a size sufficient to pass through a sieve having asieve opening of from 0.0029 to 0.0017 inch, to form a final treatingcomposition, suspending the resulting final treating composition in anaqueous carrier medium, placing said aqueous suspension against theunconsolidated formation, contacting the placed final treatingcomposition with an aqueous surface-active agent solution to water-wetthese cement particles, permitting the cement to set and form apermeable cement barrier between the formation and the well bore wherebyformation fluids can be recovered by passage through the formedpermeable cement barrier.

2. A method as claimed in claim 1 wherein the aqueous suspension of thetreating composition is placed against said formation by injecting saidsuspension at a pressure sufficient to force the aqueous suspensionagainst the unconsolidated formation.

3. A method as claimed in claim 1 wherein the treating compositioncontains from 1 to 10 percent by weight of a waterinsoluble, oleophilicmaterial of relatively high molecular weight based on the weight of thecement particles.

4. A method as claimed in claim 3 wherein said oil wetting agent is amember selected from the group consisting of a C -C aliphatic-amine,-alcohol, -acid, -amide, -glyceride, a C -C alkyl phenol, a C -C alkylnaphthol, lard, lanolin, cottonseed oil and mixtures of these materials.

5. A method as claimed in claim 4 wherein said amine is dodecylamine.

6. A method as claimed in claim 3 wherein said oil wetting agent is ahydrocarbyl amine containing l2-l 8 carbon atoms.

7. A method as claimed in claim 1 wherein said surface active agent isan ethoxylated nonylphenol containing an average of about 9.5 ethyleneoxide groups.

8. A method as claimed in claim 1 wherein the treating composition issuspended in the aqueous carrier medium in an amount of from about I to5 pounds of the treating composition per gallon of the carrier medium.

9. A method as claimed in claim I wherein the petroleum oil fraction isa refined motor lubricating oil.

10. A method as claimed in claim 1 wherein the petroleum oil fraction isa diesel oil fraction.

11. A method as claimed in claim I wherein the unconsolidated formationis washed with a salt water fraction to remove at least a portion of theunconsolidated sand particles adjacent to the well bore and to form acavity in said unconsolidated formation prior to injection of theaqueous suspension of the treating composition against said formation.

12. A treating composition suspended in an aqueous medium fraction foruse in fonning a permeable cement barrier in an unconsolidatedsand-containing oil producing formation which comprises cement, fromabout 3 to about 12 parts by weight of md particles having an averagemesh size of from about 20 mesh to about mesh, from 0.0l to about 0. 10part by weight of an oil wetting agent, from 0.3 to 0.7 part by weightof a petroleum oil fraction and from 0.02 to 0.04 part by weight of fmas] licahaving a size sufficient to pass through a sieve having a sieveopening of 0.0029 to 0.0017 inch, each per part by weight of cement,said suspended treating composition being present in an amount of fromabout i to 5 pounds per gallon of the aqueous medium.

2. A method as claimed in claim 1 wherein the aqueous suspension of thetreating composition is placed against said formation by injecting saidsuspension at a pressure sufficient to force the aqueous suspensionagainst the unconsolidated formation.
 3. A method as claimed in claim 1wherein the treating composition contains from 1 to 10 percent by weightof a water-insoluble, oleophilic material of relatively high molecularweight based on the weight of the cement particles.
 4. A method asclaimed in claim 3 wherein said oil wetting agent is a member selectedfrom the group consisting of a C10-C18 aliphatic-amine, -alcohol, -acid,-amide, -glyceride, a C10-C18 alkyl phenol, a C10-C18 alkyl naphthol,lard, lanolin, cottonseed oil and mixtures of these materials.
 5. Amethod as claimed in claim 4 wherein said amine is dodecylamine.
 6. Amethod as claimed in claim 3 wherein said oil wetting agent is ahydrocarbyl amine containing 12-18 carbon atoms.
 7. A method as claimedin claim 1 wherein said surface active agent is an ethoxylatednonylphenol containing an average of about 9.5 ethylene oxide groups. 8.A method as claimed in claim 1 wherein the treating composition issuspended in the aqueous carrier medium in an amount of from about 1 to5 pounds of the treating composition per gallon of the carrier medium.9. A method as claimed in claim 1 wherein the petroleum oil fraction isa refined motor lubricating oil.
 10. A method as claimed in claim 1wherein the petroleum oil fraction is a diesel oil fraction.
 11. Amethod as claimed in claim 1 wherein the unconsolidated formation iswashed with a salt water fraction to remove at least a portion of theunconsolidated sand particles adjacent to the well bore and to form acavity In said unconsolidated formation prior to injection of theaqueous suspension of the treating composition against said formation.12. A treating composition suspended in an aqueous medium fraction foruse in forming a permeable cement barrier in an unconsolidatedsand-containing oil producing formation which comprises cement, fromabout 3 to about 12 parts by weight of sand particles having an averagemesh size of from about 20 mesh to about 80 mesh, from 0.01 to about0.10 part by weight of an oil wetting agent, from 0.3 to 0.7 part byweight of a petroleum oil fraction and from 0.02 to 0.04 part by weightof finely ground silica having a size sufficient to pass through a sievehaving a sieve opening of 0.0029 to 0.0017 inch, each per part by weightof cement, said suspended treating composition being present in anamount of from about 1 to 5 pounds per gallon of the aqueous medium.